Searching for biomarkers and behavioral signs of early risk for neurodevelopmental disorders has emerged as an important line of clinical research in an effort to improve diagnosis and develop the most effective treatments and preventive interventions. In our research thus far, we have identified several significant differences between infants at high familial risk for Autism Spectrum Disorder (ASD) (high familial risk defined as having an older sibling with the disorder) and low risk control infants, including alterations in EEG, atypical lateralization for speech and faces, and reduced cortical connectivity all of which might serve as early risk markers. However, it is not yet known whether these risk markers extend to other infants later diagnosed with ASD,particularly infants from the general population, and whether they might also serve as risk markers for other related disorders, particularly language and social communication delay. In the current award period, we have extended the research to include a new group of infants from the general population who fail a developmental screener at 12 months. In this project, we include an additional cohort of children with Down syndrome (DS). Children with DS are known to have cognitive impairment, as well as disproportionate impairment in communication skills. However, there is substantial heterogeneity and individual differences in language and social outcomes. Language impairments can range from mild articulation deficits to minimal / no use of verbal language, and up to 18% of children with DS also meet criteria for co-occurring ASD. In this project, we will recruit 30 children with DS, ages 12-36 months, who will undergo a battery of electrophysiological and behavioral measures at a single study visit. The project will address two specific aims: The first aim is to investigate whether neural and behavioral risk markers that have been found to distinguish infants at risk for developmental concerns extend to young children with DS. We hypothesize that some risk markers seen in high risk groups will also be seen in children with DS. The second aim is to investigate the relationships between EEG findings and developmental and behavioral phenotypes in DS. We hypothesize that within the DS group, we will detect differences in EEG patterns that will correlate with language and social communication phenotype. As research progresses on identifying behavioral and neural markers in infants that are at risk for neurodevelopment disorders, it is critical that we extend our research to include individuals with known genetic syndromes and that we advance our knowledge of shared and unique mechanisms of development. Inclusion of individuals with DS, which has a well-described characteristic language and communication phenotype as well as increased risk of ASD, may provide a unique opportunity to better understand pathways leading to variation in outcome.